This story is about Sawamura Seiji, a chivalrous, though delinquent, high school student, who is popular among younger students. However, because of his bad reputation, he spends his youth without a girlfriend. His lonely life is thrown into upheavel when, all of a sudden, a girl appears in place of his right hand!
The girl's name is Kasugano Midori. She is very shy and has secretly been in love with Seiji for a long time. In the face of this strange circumstance, she keeps on believing in herself wholeheartedly as Seiji's right hand lover. As a consequence, Midori now lives together with Seiji and the two begin to live they're grotesque co-existence together in secrecy!
From animenfo.com